ORTHOSOMELLA LAMBDINAE N-SP (MICROSPORIDA, UNIKARYONIDAE) FROM THE SPRING HEMLOCK LOOPER, LAMBDINA-ATHASARIA (LEPIDOPTERA, GEOMETRIDAE)

A new species of microsporidia, Orthosomella lambdinae n. sp. (Microsp orida: Unikaryonidae), is described from larvae of the spring hemlock looper, Lambdina athasaria (Lepidoptera: Geometridae). The principal s ite of infection is the midgut epithelium. The microsporidium is free within the hyaloplasm of the host cell and has unpaired nuclei in all stages of development. Schizonts are rounded to irregular in shape wit h a variable number of nuclei (2-29, median = 6). They are limited by a simple plasmalemma and divide by plasmotomy. Sporogonial plasmodia a re elongate and sausage-shaped with a variable number (2-18, median = 6) of linearly arranged nuclei. They are surrounded by an electron-den se surface coat and give rise to moniliform chains of uninucleated spo roblasts with a corresponding number of nuclei. Sporoblasts concurrent ly undergo sporogenesis prior to cytoplasmic cleavage into free spores . Mature spores are uninucleate and oblong to slightly reniform. They measure 2.8 x 1.5 mu m (live) and have 7-8 turns of the polar filament . The natural prevalence of O. lambdinae in larval populations of L. a thasaria was found to range from 2.0 to 18.4% (6.8% overall). (C) 1996 Academic Press, Inc.